During the manufacture of semiconductor wafers and/or LCD panels, such as are used in flat panel television sets, a substrate is exposed to gas in which an electrically generated plasma is formed. The gas enters from a “showerhead” like fixture positioned above the substrate, which also functions as one of the electrodes to form the plasma. In order to maximize yield, it is important that the distance from the showerhead to the substrate be consistent across the entire substrate surface. In other words, it is important that the plane of the substrate surface and the plane of the showerhead be parallel. It is, accordingly, very important in the setup of the semiconductor processing tool where the process takes place that the relative positions of the showerhead and substrate, or the “platen” that holds the substrate, be adjusted to be parallel. This requires the ability to measure the relative positions of the showerhead and substrate, particularly, the distance between them at various points, which can yield a measure the parallelism of the two.
One way that such distance/parallelism measurements have been performed in the past was by using a measurement device that was placed on the platen under the showerhead. Such measurement devices typically included compressible internal springs. The measurement device would rest on the platen and contact the showerhead, and be compressed as the showerhead was lowered. In the lowered state of the showerhead, the thickness of the measurement device at any point is the distance between the platen and the showerhead. Measuring equipment inside the measurement device would measure the thickness of the device, thereby measuring the distance from the platen to the showerhead. Measurements thus made at multiple points between the platen and the showerhead were able to provide an overall measure of parallelism of the platen and showerhead. However, such a device, in its uncompressed state, was generally larger than the nominal distance between the platen and the showerhead. Accordingly, it was necessary to compress the measurement device before placing the device on the platen, or else the showerhead would have to be removed first. Additionally, these measurement devices generally provided information relative to the parallelism using a cable that ran out of the semiconductor processing chamber door to a display device. The cable was flat and able to pass through the door even when the door was closed, as it is necessary that the measurements are made, and adjustments performed, when the processing chamber is closed. The cable was generally prone to failure because it passed through and was compressed in the seal of the door.
Accordingly, there was a need to perform the measurement and data display without cable. More recently, techniques for sensing conditions within a substrate processing system using wireless communication have been developed. U.S. Pat. No. 6,468,816 reports a method for sensing conditions within a substrate processing system. That reference discloses the ability to sense a variety of conditions within the processing system. The reference also provides a distance probe which can ensure that the wafer surfaces are both parallel to and at the proper distance from the target or showerhead of the process chamber. The distance probe is disclosed to include contacting sensors or electro-optical sensors arranged at a number of locations on the surface of the probe platform to determine the distance from and angle of inclination between the probe and the target or showerhead. While such advances have assisted in the setup and operation of the semiconductor processing tools, the provision of the extremely low-profile distance sensor has been lacking.
Yet another problem with respect to the adjustment of parallelism of a platen with respect to a showerhead of a semiconductor processing tool is the requirement that a technician monitor from three to eight individual distance measurements while adjusting the orientation and elevation of the platen relative to the showerhead or target. It was generally not practical to provide platen or showerheads or targets that were perfectly flat, so it was generally not possible to adjust the platen so that all of the distance measurements were the same. Accordingly, a technician's judgment was relied upon to determine when the adjustments were “good enough.”
Accordingly, there exists a continuing need for extremely low-profile distance/parallelism sensing within a semiconductor processing tool, as well as better methods for automatically measuring and adjusting the distance between the platen and showerhead of a semiconductor-processing tool.